The present invention relates to a method of driving volatile impurities from a ground by means of air which is aspirated together with the gases from a shaft provided in the ground with impurities and having a gas-permeable shaft wall, wherein openings for afterflow of air from outside are provided. The present invention also relates to an arrangement for driving volatile impurities from a ground by means of air.
A method of and an arrangement for driving volatile impurities from a ground of the above mentioned general type are disclosed in the German patent application P 3,626,145.9. This method and arrangement are very effective. However, it is to be understood that they can be further improved in some aspects.
Efforts have been undertaken for improving the efficiency of the method during driving of impurities of very dense and muddy soils, where the dense soil allows the afterflow of air only in a small quantity and correspondingly during the increase of the negative pressure in the shaft only an insufficient flow speed in the shaft and soil can be achieved. Physical considerations however show that the air which serves for taking the volatile impurities in gas form must have a predetermined minimum flow speed for achieving an entrainment of the impurities. An increase of the negative pressure in the suction shaft means both an increased energy consumption which puts in question the efficacy of the method, and also the grave disadvantage in that with the use of negative pressure generators, the aspirated gas/air mixture is so significantly heated that for example the aspirated chlorine hydrocarbons become unstable and can be converted in highly toxic substances.